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Jabiru 3300 Over Voltage
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user9253

Joined: 28 Mar 2008
Posts: 1938
Location: Riley TWP Michigan

Posted: Wed Mar 14, 2012 12:06 am Post subject: Re: Jabiru 3300 Over Voltage

Good points Noel.  In Rich's airplane, the alternator is actually a permanent magnet dynamo.  There are no field coils or brushes.

  Rich, You mentioned in an earlier post that the circuit breaker was cool only when the voltage sense wire is connected directly to the battery.  That tells me that the voltage regulator sense wire is carrying excessive current.  That is another indication that the regulator is bad.

  Heat could be causing the regulators to fail.  I suggest that a shroud be installed over the regulator and that cooling air be forced into the shroud with 5/8" duct.

Joe

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Joe Gores

nuckolls.bob(at)aeroelect
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Posted: Wed Mar 14, 2012 12:29 pm Post subject: Jabiru 3300 Over Voltage

At 09:37 PM 3/13/2012, you wrote:


 > Have you seen any data source that argues with what's shown above?



No, I was going by Rich's schematic that shows the lamp connected to 

the outside terminal of the voltage regulator.  But now Rich has 

explained that his drawing is a schematic and not a wiring 

diagram.  He is confident that the voltage regulator is wired 

correctly.  I believe him.



         Okay.



I see 3 possible causes for the high voltage:

1. There is a wiring error.

2. There is an intermittent high resistance connection between the 

main bus and the ignition terminal of the regulator, or between 

regulator ground and aircraft ground.



         I like this one.  The whole purpose of a

         dedicated sense lead is to prevent a sharing

         of operating currents with measurement currents.

         Obviously, the negative lead of the regulator

         output is the case ground . . . which is also

         the negative sense lead!

         I'd go for an experiment to un-mount the regulator

         from it's present location, attach a robust ground

         lead from regulator case to ship's single point

         ground. 10AWG would be good. Then go fly it and

         see what the voltage does.



3. The voltage regulator is bad.



         Maybe . . . but 'bad' regulators generally work

         or don't work. This regulator is behaving like it

         it is in distress but not failed.

_

Due to the fact that the 5amp circuit breaker gets warm, I suspect 

the voltage regulator is bad.



         It would be interesting to see what kind of

         breaker he's using. The size of the heater in

         a miniature breaker is so small



http://aeroelectric.com/Pictures/Breakers/Klixon_1.jpg



         I cannot imagine how you get a enough continuous

         load to 'warm' the breaker. Let's say you get

         4.9999 amps flowing in the breaker to 'warm' it up

         without tripping it. This implies that some soft

         fault downstream of the breaker is dissipating

         4.999 x 14 = 70 watts! That amount of energy being

         dumped inside the regulator would probably get

         you some form of gross failure or at least some

         bad smells.

   It seems to me that the voltage between the regulator ground 

terminal and the regulator voltage-sense terminal should never go 

above the set point (14.2).  If it does, then the regulator is not 

doing its job, regardless of any loose connections elsewhere.



         Exactly . . . and the ground lead is highly

         suspect.



The voltage is still too high, even with the voltage-sense wire 

connected directly to the battery.  That eliminates the circuit 

breaker and the master switch as potential problems.



Bob, please correct me if my reasoning is faulty.  Just do not tell 

my wife that I made a mistake.



         Sounds good so far.

   Bob . . .

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user9253

Joined: 28 Mar 2008
Posts: 1938
Location: Riley TWP Michigan

Posted: Fri Mar 23, 2012 5:42 am Post subject: Re: Jabiru 3300 Over Voltage

Rich,

Did you ever solve the high voltage problem?  Did you try adding a robust ground lead from regulator case to ship's single point ground as Bob Nuckolls suggested?  Or was the regulator bad?  I am curious to know the answer.

Joe

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Joe Gores

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